Auto merge of #10495 - ehuss:remove-profile-panic-inherit, r=weihanglo

Auto merge of #10495 - ehuss:remove-profile-panic-inherit, r=weihanglo

Remove unused profile support for -Zpanic-abort-tests

This removes the vestigial `PanicSetting::Inherit` setting.

This was initially introduced in #7460 which added `-Zpanic-abort-tests`. This was needed at the time because `test` and `dev` profiles were separate, but they were inter-mixed when running `cargo test`. That would cause a problem if the unwind/abort settings were mixed.  However, with named profiles, `test` now inherits from `dev`, so this is no longer necessary. Now that named profiles are stable, support for the old form is no longer necessary.